The present invention relates to optical communication, generally, and more particularly to wavelength converters.
Dense wavelength division multiplexing (xe2x80x9cDWDMxe2x80x9d) systems provide numerous wavelength channels for optical communication. DWDM systems employ wavelength converters for rearranging and reallocating wavelength channels in a single optical wavelength band. For the purposes of the present disclosure, the phrase xe2x80x9cwavelength bandxe2x80x9d refers to a distinct portion of the optical spectrum having a wavelength width of approximately 100 nm.
With the growth in network interconnectivity, a new application for wavelength converters has emerged. Wavelength converters are now being used for interfacing short haul communication applications, in the 1300 nm wavelength band, with long haul communication applications, in the 1500 nm wavelength band. To date, wavelength converters for interfacing communication applications have employed an optical-to-electrical-to-optical design. Converting an optical data signal to an electrical data signal and back into an optical data signal, however, has posed limitations on data transmission rates. Presently, optical-to-electrical-to-optical wavelength converters have reached data transmission rates of approximately 620 MB/s.
Given these limitations, considerable research has been expended on developing a wavelength converter having an optical-to-optical design. One such optical-to-optical wavelength converter has been proposed by Barnsley and Fiddyment, in IEEE Photonics Technology Letters, Vol. 3, No. 3, March 1991 (hereinafter xe2x80x9cBarnsleyxe2x80x9d). Barnsley suggests an optical-to-optical wavelength converter for converting an optical data signal from a first wavelength in the 1300 nm wavelength band to a second wavelength in the 1500 nm wavelength band. It is believed, however, that Barnsley""s device generates amplified spontaneous emission in the 1500 nm wavelength band. Thus, Barnsley""s optical-to-optical converter apparently introduces noise in the same wavelength band as that of the converted optical data signal.
Another optical-to-optical converter has been proposed by Ma et al., in IEEE Photonics Technology Letters, Vol. 11, No. 2, February 1999 (hereinafter xe2x80x9cMaxe2x80x9d). Ma suggests an optical-to-optical wavelength converter for converting an optical data signal from a first wavelength in the 1500 nm wavelength band to a second wavelength in the 1500 nm wavelength band. It is believed that Ma""s optical-to-optical wavelength converter is intended to support the rearrangement and reallocation of wavelength channels in the 1500 nm wavelength band.
Ma""s optical-to-optical wavelength converter appears to comprise a directional coupler having a first waveguide for receiving an optical data signal at a first wavelength in the 1500 nm wavelength band and a second waveguide for receiving a continuous wave optical signal at a second wavelength in the 1500 nm wavelength band. From Ma""s disclosure, it is believed that the continuous wave optical signal is coupled from the second waveguide to the first waveguide in response to a binary zero in the original optical data signal, while the continuous wave optical signal continues to propagate through the second waveguide in response to a binary one in the original optical data signal.
Ma""s optical-to-optical wavelength converter, however, has several shortcomings. First, it is believed that Ma""s optical-to-optical wavelength converter is intended to assist in the management of long haul communication traffic by preventing the collision of two or more incoming optical data signals having the same wavelength in the 1500 nm wavelength band. As such, Ma""s device appears limited to converting wavelengths within the same wavelength band. For example, the optical-to-optical wavelength converter of Ma apparently cannot convert optical signals from a first wavelength in the 1300 nm band to a second wavelength in the 1500 nm wavelength band. If the optical bits at the first wavelength in the 1500 nm wavelength band of Ma""s proposal are replaced with optical bits at a wavelength in the 1300 nm wavelength band, it is believed that the continuous wave optical signal in the 1500 nm wavelength band would likely continue to couple from the second waveguide to the first waveguide, irrespective of the binary values of the optical data signal in the 1300 nm wavelength band.
Further, the response characteristics, such as the signal to noise ratio, of Ma""s optical-to-optical converter are apparently sub-optimal. The device of Ma appears to create amplified spontaneous emission in the 1500 nm wavelength band. As such, it is believed that Ma""s optical-to-optical converter introduces noise in the same wavelength band (1500 nm) as that of the converted optical data signal (1500 nm).
It also appears that Ma""s device has specific power requirements. Apparently, Ma""s continuous wave optical signal must be lower in power than the original optical data signal for proper operation. If the continuous wave optical signal is relatively close in power to the original optical data signal, it is believed that that the continuous wave optical signal would likely continue to couple from the second waveguide to the first waveguide, irrespective of the binary values of the original optical data signal.
Consequently, a need exists for an optical-to-optical wavelength converter for converting an optical data signal from a first wavelength in the 1300 nm band to a second wavelength in the 1500 nm wavelength band having a data transmission rate greater than 620 MB/s. There is also a need for an optical-to-optical wavelength converter, which does not introduce noise, such as amplified spontaneous emission, in the wavelength band of the converted optical data signal. A need also exists for an optical-to-optical wavelength converter employing a continuous wave optical signal, which need not be lower in power than the original optical data signal.
We have invented an optical-to-optical wavelength converter for converting a plurality of optical bits from a first wavelength in a first wavelength band to a second wavelength in a second wavelength band. For the purposes of the present disclosure, the phrase xe2x80x9cplurality of optical bitsxe2x80x9d refers to a digital data stream optically encoded using a modulation scheme, such as amplitude shift key modulation, for example.
In contrast with known prior art, our optical-to-optical wavelength converter does not introduce amplified spontaneous emission noise in the wavelength band of the converted plurality of optical bits. Further, the continuous wave optical signal, as employed with our invention, need not be lower in power than the plurality of optical bits to be converted, unlike the known prior art. Our optical-to-optical wavelength converter also supports a data transmission rate substantially greater than 620 MB/s.
In an illustrative embodiment of the present invention, an optical-to-optical wavelength converter comprises a directional coupler. The directional coupler comprises at least one optical element, such as, for example a semiconductor optical amplifier. The optical element has an index of refraction, which changes in response to optical power substantially in the first wavelength band.
These and other embodiments, advantages and objects will become apparent to skilled artisans from the following detailed description read in conjunction with the appended claims and the drawings attached hereto.